Co-owned U.S. Pat. No. 5,492,098 to Hafner, et al., describes a hydraulically-actuated fuel injector having rate shaping through fuel spillage. Like many hydraulically-actuated fuel injectors, Hafner includes a pumping element or plunger that defines a portion of a fuel pressurization chamber. In order to produce a split injection at an idle condition, the Hafner, et al. plunger includes an annulus in fluid communication with the fuel pressurization chamber via several internal passageways. As the plunger is driven downward, the annulus comes briefly into registry with a spill passage defined by the injector body. When this occurs, fuel spills from the fuel pressurization chamber, and fuel pressure drops below a valve closing pressure sufficient to allow the nozzle needle valve to briefly close. In order to produce a split injection at idle, the plunger annulus is out of registry with the spill passage for the beginning and end portions of the plunger's stroke.
In part to increase the operating range of the Hafner, et al. injector, the actuation fluid pressure supplied to the injector is adjusted to be relatively low at idle but relatively high at rated conditions. These differing pressures allow the injector to inject a very small amount of fuel at idle, but a relatively large amount of fuel at a rated condition. This actuation fluid pressure difference also results in the plunger moving at significantly different rates at idle and rated conditions. Because the plunger moves relatively slowly at the idle condition, the plunger annulus is in registry with the spill passage for a sufficient duration that a split injection can occur; however, because the plunger moves so quickly at a rated condition, the plunger annulus moves past the spill passage so quickly that very little spillage occurs and no split injection takes place. Because of the stroke length limitations available for the Hafner, et al. plunger, it would be difficult to modify in a way that could produce a split injection, or other significant rate shaping completely across its operating range. Although the Hafner, et al. injector has performed magnificently for many years, there remains room for improvement in providing a broader possible range of rate shaping at various operating conditions.
The present invention is directed to providing more flexibility and control to rate shaping through fuel spillage in hydraulically-actuated fuel injectors.